Synthesis, characterization and catalytic activity of transition metal ...

ash in an alkaline solution, followed by crystallisation to form the ring like structures that are
necessary for zeolite construction. The high percentage of aluminosilicates in fly ash makes them
a cheap and readily available source of Si and Al for zeolite synthesis. The low Si/Al ratio of fly
ash allows for the synthesis of low Si zeolites, which have a high cation exchange capacity, high
affinity towards polar molecules and a large pore volume [16].
Homogeneous catalysts can offer high molar catalytic efficiencies and rates under mild
conditions, tolerance to many types of organic functionality and high selectivity in reactions that
allow formation of specific desired reaction product. Heterogeneous catalysts are usually more
robust (insensitive to air and moisture), easy to handle and can be completely removed from the
reaction easily. An ideal catalyst would possess the beneficial aspects of both homogeneous and
heterogeneous systems. Towards this objective, significant work has been expanded in an attempt
to develop homogeneous catalysts that have been anchored to a solid support though it is
associated with multiple practical difficulties. Encapsulation of transition metal complexes in
zeolites and related materials has gained much attention since they possess both homogeneous and
heterogeneous catalytic characters. The rigid inorganic zeolite framework defines the reaction
cavity surrounding the active sites of the transition metal complexes. Though the encapsulation of
transition metal complexes in zeolites have been established as good catalysts, the replacement of
commercial zeolites by FAZ has gained only little attention. Recently, encapsulation of N,N′-
ethylenebis(salicylamide) metal complexes in fly ash based zeolite was reported and these
complexes have been found to catalyze the liquid phase hydroxylation of phenol with hydrogen
peroxide [17]. Up to now, hydroxylation of phenol with hydrogen peroxide as the oxidant has
become the most general way to obtain diphenols owing to its environmental acceptability. The
activity of the encapsulated transition metal complexes is different from that of the neat
complexes since the selectivity is altered in a constrained environment [18-20] Results from the
present study seems promising enough to introduce the transition metal complexes encapsulated
zeolites as catalysts for the liquid phase hydroxylation of phenol. However, more investigations
are recommended to confirm the industrial applicability of the obtained results, especially
concerning the total efficiency and economics.
This work involves the (i) the synthesis of zeolite from fly ash (ii) characterisation of the
synthesized FAZ (iii) encapsulation of transition metal-ascorbate complexes in the zeolite cavities
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